MOSFETs are commonly used for fast switching in electronic circuits. However, where the load is inductive the switching speed is limited due to the intrinsic body diode problem. When the gate voltage is used to switch MOSFET from ON to OFF state (reverse recovery), the intrinsic p-n junction diode has to conduct current, and will inject carriers into the bulk of device. Until the injected carriers are dissipated, the MOSFET will continue to stay in the ON state. This causes slow switching of MOSFET from ON to OFF state and limits the frequency of the MOSFET operation.
To overcome the slow switching of the body diode an external freewheeling diode is often added between the source and the drain of the MOSFET to prevent the injection of carriers during reverse recovery. However, the addition of the external diode can lead to increased EMI, since the current that was flowing through the MOSFET now has to flow through the external diode and connecting wires. The extra EMI emissions can also limit the switching speed of the MOSFET with freewheeling diode. While the freewheeling diode is typically put as close to MOSFET as possible, the problem of extra EMI remains.
While integrating the P-N junction diode technology into the MOSFET has an initial appeal, this technology has a limited potential to improve the body diode problem, since the body diode is a P-N junction diode integral to MOSFET structure. Similarly, Schottky diode technology is practically incompatible with MOSFET technologies, since it requires specific metallization not well suited for MOSFET manufacturing.